Selenium rectifier temperature indicator



Sept. 4, 19 5- G. H. SHOEMAKER 2,334,200

SELENIUM RECTIFIER TEMPERATURE INDICATOR Filed May 1, 1945 IN VEN TOR.GEO/P65 H. Sf/OfMA/ff/P Patented Sept. 4, 1945 FFlCE I SELENIUM REC IElfin; TUBE IOATOR George H. Shoemaker, Brooklyn, N. Y., gnor to FederalTelephone & o Corporation, New York, N. Y., a corporation of DelawareApplication May 1, 1943, Serial No. 485,379

4 Claims. (Cl. 175-366) in thereverse direction and provide the recti- 1tying action.

Selenium rectifier discs are subject to heating during operation, causedby the resistance oiiered .by the plates themselves to the passage ofcurrent. The mammumtemperature to which the disc may safely rise isgoverned by the melting point of the most readily fusible component ofthe rectifier, which is usually the metallic counter-electrode. It isfrequently desirable to measure the temperature of the disc while it isin use to learn how close it is to the maximum safe temperature andtherefore whether the input current can be increased. According to myinvention I do this by leaving a small area of the selenium layer freeof the metallic counter=electrode, to which exposed area of selenium Iattach a pyrometer or thermocouple.

By this arrangement there is no injury to the barrier layer beneath thecounter-electrode and consequently no danger of short circuit; and byuse of the pyrometer or thermocouple an indication of the temperature ata hot part of the element can readily be had.

The invention will be better understood from the following detaileddescription and the attached drawingrof which;

Figure 1 is a cross-section view of a selenium rectifier disc having asmall area of exposed selenium surface in contact with the junction of athermocouple;

Figure 2 is a plan view of the same. Figure 1 shows the usual type ofselenium rec--' tifier disccomprising a'base plate i which may tapeabout 1 6" in diameter over this area of selenium layer before spraying.I then spray the alloy on the selenium layer whereupon all but the areaprotected by the tape receives a coating. When the spraying operation iscomplete I remove the tape and fuse the junction i of a ther= mocoupleto the exposed selenium surface by applying a hot point to the junctionand pressing it down into the selenium. which softens. The thermocouplemay be conveniently made by twisting a copper wire and a constantan wiretogether (indicated by 6 and i) and heating the end 5 to conform to thesurface of the selenium to which it is fused. The junction is extremelythin and may be somewhat oval in shape. During the fusing care must betaken to see that the junction does not sink deep enough in the seleniumlayer to contact the plate beneath the selenium, and care should betaken that no exposed metal of the thermocouple touches thecounter-electrode. It may be desirable to spray the thermocouple arealightly over with varnish. An indication of the temperature may beobtained in a well-known manner by connecting a meter such as agalvanometer in circuit with the thermocouple.

I do not wish to be limited to athermocouple as a means for measuringthe temperature, but contemplate the use of any electrical pyrometersuch as the platinum resistance pyrometer of similar device for thispurpose.

What I claim is:

1. A selenium rectifier element comprising a base plate, a layer ofselenium placed over a surface of said base plate, a counter-electrodeplaced over said selenium layer so as to leave exposed a small area ofsaid selenium layer, and a thermo-v couple junction fused to the saidexposed area of said selenium layer.

2. The method of making a selenium rectifier element which comprisesforming a layer of selenium on a base plate, applying a covering over asmall area of the surface of said selenium, ap-

plying a counter-electrode on said selenium layer and around saidcovering, removing said covering and fusing a thermocouple in theexposed area of the selenium surface from which the covering wasremoved. I

8. The method of mag a selenium rectifier element which comprisesforming a layer of selenium on a base plate, applying a cove over ientlybe done by applying a piece of adhesive a small area of the surface ofsaid selenium, ap-- plying a counter-electrode on said selenium layerand around said cove, removing said covering and fusing an electricalheat responsive device to the exposed area of the selenium sun'ace fromwhich the covering was removed.

4. A selenium rectifier element comprising a base plate, a layer ofselenium placed over a surface of said base plate, a counter-electrodeplaced over said selenium layer so as to leave exposed a small areaofsaid selenium layer. an electrical heat responsive device embedded insaid exposed area 01' said selenium layer, and a protective insulatinglayer covering said heat re- 5 sponsive device.

GEORGE H. SHOEMAKER.

